After injury the liver will undergo controlled compensatory growth restoring the organ to its original mass. Remarkably precise mechanisms must control this process, sensing the requirement for growth and stopping it when the correct size is reached. However, chronic regeneration or prolonged treatment with a variety of agents will overcome this control, leading to tumorigenesis. Liver regeneration is accompanied by changes in gene expression, including the expression of the alpha-Fetoprotein (AFP) gene. AFP is a so called fetal antigen--expressed during fetal life, but not after birth, then expressed again during liver regeneration and tumorigenesis. The level of AFP expression in liver regeneration is controlled by the genetic locus, Rif, specifying lower AFP mRNA levels in C57BL/6 mice during regeneration. The biological significance of this observation is unknown, but it does correlate with differences in I susceptibility to tumorigenesis. The long term goal is to understand differences in gene regulation during controlled regenerative growth versus uncontrolled tumorigenic growth. The AFP gene will be used as a model for genes expressed during liver regeneration and tumorigenesis. It will first be determined if the increase in AFP mRNA levels during liver regeneration is the result of transcriptional or post-transcriptional activities, by direct measurement of the number of transcripts produced over time. Which regions of the locus are responsible for the increase levels of AFP during liver regeneration? Mice carrying transgenes consisting of regions of the AFP locus driving expression of a marker gene will be tested for expression during liver regeneration. This strategy will localize the region required, permitting the use of in vitro techniques to identify and clone the factor(s) responsible for gene expression. The chromatin surrounding active genes usually differs from inactive genes in its nuclease sensitivity, as a result of transcription factor binding. Nuclease hypersensitive sites will be mapped and compared to those already found in the normal adult and fetal liver. Are the strain dependent differences in mRNA levels a part of the mechanism of induction, or is it separate, reflecting other differences in gene expression. This will be addressed by experiments comparing results for 2 mouse strains C57BL/6 and C3H/He.